Antisera against bombesin, substance P, methionine enkephalin and met5-enkephalin-Arg6-Phe7 were used to study the distribution of these peptides in the brain, spinal cord and peripheral organs. Bombesin was found in several cell groups in the brain. One of the major groups in the paraventricular nucleus of the hypothalamus did not exhibit substance P-like immunoreactivity though in several other areas like the nucleus tractus solitarii, dorsal parabrachial nucleus and dorsolateral tegmental nucleus immunoreactivity was found in the same cell groups. In the periphery, bombesin-like immunoreactivity was found in the spinal sensory ganglia, adrenal medulla and nerve fibres innervating the lung. Met5-enkephalin Arg6-Phe7-like immunoreactivity was found in the same areas of the brain as met-enkephalin.